Book contents
- Frontmatter
- Contents
- Preface
- 1 Energy Transfers in Cyclic Heat Engines
- 2 Mechanism Effectiveness and Mechanical Efficiency
- 3 General Efficiency Limits
- 4 Compression Ratio and Shaft Work
- 5 Pressurization Effects
- 6 Charge Effects in Ideal Stirling Engines
- 7 Crossley–Stirling Engines
- 8 Generalized Engine Cycles and Variable Buffer Pressure
- 9 Multi-Workspace Engines and Heat Pumps
- 10 Optimum Stirling Engine Geometry
- 11 Heat Transfer Effects
- Appendix A General Theory of Machines, Effectiveness, and Efficiency
- Appendix B An Ultra Low Temperature Differential Stirling Engine
- Appendix C Derivation of Schmidt Gamma Equations
- References
- Index
11 - Heat Transfer Effects
Published online by Cambridge University Press: 15 October 2009
- Frontmatter
- Contents
- Preface
- 1 Energy Transfers in Cyclic Heat Engines
- 2 Mechanism Effectiveness and Mechanical Efficiency
- 3 General Efficiency Limits
- 4 Compression Ratio and Shaft Work
- 5 Pressurization Effects
- 6 Charge Effects in Ideal Stirling Engines
- 7 Crossley–Stirling Engines
- 8 Generalized Engine Cycles and Variable Buffer Pressure
- 9 Multi-Workspace Engines and Heat Pumps
- 10 Optimum Stirling Engine Geometry
- 11 Heat Transfer Effects
- Appendix A General Theory of Machines, Effectiveness, and Efficiency
- Appendix B An Ultra Low Temperature Differential Stirling Engine
- Appendix C Derivation of Schmidt Gamma Equations
- References
- Index
Summary
This chapter continues the examination of the limits on Stirling engine performance by taking into consideration, with the mechanical losses already covered, thermal limitations and losses from which real Stirling engines suffer. First covered is limited heat transfer rate into and out of the working fluid of the engine. This is modeled here just as Curzon and Ahlborn did for Carnot engines (Curzon & Ahlborn, 1975). In addition, introduced later in the chapter is an internal heat leak through the engine from the hot to the cold section governed by the same heat transfer regime. This simulates in a general way the various internal thermal losses occurring in real Stirling engines.
HEAT EXCHANGE
Thermal energy must be transferred into and out of a Stirling engine via heat exchangers at the hot and cold ends. A temperature gradient is required to drive the transfer; in other words, there must be a temperature differential between the source reservoir and the working fluid when it receives thermal energy. Likewise, a temperature difference is required between the engine working substance and the sink reservoir in order for the engine to reject thermal energy. The larger these differences, the greater the rate of energy transfer. This aspect of heat transfer is modeled in a general way by Newton's Law of Cooling (Bejan, 1996b).
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- Information
- Mechanical Efficiency of Heat Engines , pp. 117 - 134Publisher: Cambridge University PressPrint publication year: 2007